Base for an air filter



FIG. 1 is a downward looking perspective view of the base for an air filter, with the view from the diametrically opposing side being the mirror image thereof;

FIG. 2 is an upward looking perspective view of the base for an air filter of FIG. 1, with the view from the diametrically opposing side being the mirror image thereof; and,

FIG. 3 is a sectional view taken along section 3-3 of FIG. 2, showing a cross section of the base.

The broken lines show the environment of the base and represent unclaimed subject matter and form no part of the claimed design. 

CLAIM The ornamental design for a base for an air filter, as shown and described. 